Sonic atomizer for liquids



Sept. 10, 1963 Filed Nov. 9. 1961 R. J. LANG 3,103,310

some ATOMIZER FOR LIQUIDS 4 Sheets-Sheet 1 Robert J. Long Inventor Patent Attorney Sept. 10, .1963 R. LANG 3,103,310

SONIC ATOMIZER FOR LIQUIDS Filed Nov. 9, 1961 4 Sheets -Sheet 2 ELECTRIC MOTOR FIGURE 2 Robert J. Long Inventor Patent Attorney Sept. 10, 1963 R. J. LANG some ATOMIZER FOR LIQUIDS 4 Sheets-Sheet 3 Filed Nov. 9, 1961 FIGURE 3 IIO Inventor Robert J. Lung Byw 7 Patent Attorney Sept. 10, '1963 R. J. LANG 3,103,310

. SONIC ATOMIZER FOR LIQUIDS Filed Nov. 9, 1961 4 Sheets-Sheet 4 FIGURE 4 FIGURE 5 Robert J. Long Inventor Po tenf Attorney United States Patent :Oflice 3,103,310 Patented Sept. 10,1963

3,103,310 SONIC ATOMIZER FOR LIQUIDS Robert J. Lang, Watchung, NJ-, assignor to Esso Research and Engineering Company, a corporation of Delaware I Filed Nov. 9, 1961, Ser. No. 152,712 4 Claims. (Cl. 239-4) States Patent 'Oflice on December 31, 1959, now aban doned.

It is well known in the art that atomization of liquids may be effected through the use of sonic energy. A pertinent reference is the article Ultrasonic Atomization of Liquids by l. N. Antonevich appearing at pp. 6-l5 of Transactions on Ultrasonics, February, 1959, published by the Institute of Radio Engineers. One apparatus which has been used for atomizing liquids is a transducer comprising a piece of ceramic piezoelectric material such as barium titanate bonded on a flat surface to the larger diametral surface of a truncated conical resonator of an elastic and electrically conductive material such as aluminum. In a particular apparatus, the ceramic piece is in the form of a disc having two flat, substantially parallel faces. Assuming proper sizing of this assembly, the governing criterion of which will be discussed subsequently, and assuming further that an alternating voltage of relatively high frequency is applied across the flat faces of the ceramic disc, the disc will be cyclically thick ened and thinned and will generate alternate compression and rarefaction waves of sonic energy.

lhis sonic energy, which may be characterizedby a frequency above the range of normal hearing, will cause a cyclical lengthening and shortening or longitudinal vibration of the metal resonator as it flows thereinto. With decreasing cross-sectional area of the resonator in the direction away from the ceramic disc or piezo-electric element, there will be a concentration of energy. toward the resonator tip and an increasing amplitude of motion. If a drop of liquid such 138 home heating oil be applied to the resonator tip or to a relatively thin and flexible plate afi'ixed thereto While the resonator is being vibrated longitudinally, sonic energy will flow into this drop and the drop will be broken up into a fog of fine particles; that is, will be atomized.

Sizing of the sonic atomizing apparatus will now be considered. In considering this, it should be borne in mind that for a given temperature the speed of sound in a solid material has an essentially fixed value. This speed is the product of sonic Wave frequency and the length of the wave or wavelength. Corresponding to an increasing frequency there must be a decreasing wavelength and vice versa. For apparatus of the class described comprising a thin disc of ceramic material bonded to the base of a truncated metal cone, which apparatus may be referred to as being of the half-wave variety, the

length of the assembly from the tip of the cone to the more distant face of the ceramic disc should be very nearly equal to one half of the wavelength of sound in the material of the cone at the operating frequency. This assumes that the thickness of the disc is quite small compared to the length of the cone. I

stance is not peculiar to half-wave apparatus only. Similar considerations apply in the design of full-wave sonic apparatus also. In, the latter apparatus a ceramic sleeve or cylinder is bonded at one of its ends to the base of a metal cone. The lengths of the sleeve and cone are respectively equal to one-half the wavelength of-sound in their particular materials at the operating frequency se lected. Such apparatus is illustrated and described, for example, in US. Patent No. 2,514,080 to W. P. Mason, issued July 4, 19-50} What ever the apparatus used for sonic atomization of liquids, therefore, the question of the relation, if any, between the frequency of sonic energy applied and the size of liquid particlegeneratedbecomes an important one, assuming a particular particle size is needed or desired, out of consideration of the effect of sonic energy frequency on the sizing of apparatus elements. T0 provide a basis for answering this question, some fundamental principles and experimental data relating to the atomization of liquids by sonic energy means will be reviewed. 7 q

The mechanism by which direct sonic energy atomization of liquids takes place involves the formation of tiny standing waves at the surface of the liquid. When sonic energy is propagated through a liquid and disturbs its surface, two wave trains are formed at right angles to each other. These trains combine into an interference pattern which comprises many small conical protuberancesat the liquid-air interface. If the sonic energy concentration be sufiiciently intense, the height of these protuberances will increase to approximately one half of the length of the waves from which they are formed, and droplets or liquid particles will be ejected from their peaks. In this manner a fog will be formed in the air above the liquid.-

Length of surface waves on a liquid being sonically energized is a function of sonic frequency. With increasring frequency there will be decreasing wavelength. The

or, expressing the several factors in their usual symbolsi Experimental detenminations have shown wavelength 1 values calculated according-toEquation 2. to be substantially accurate.

Depending on the use to which a liquid broken up or dogged by sonic energy is to be put, a fuel to be mixed with air and then ignited, for example, the fog. particle size to which the liquid is atomized, will be of great importance. For fuel combustion purposes it is-des'irable that the particles be very fine indeed. Experiments have been conducted to determine a relationship between particle size and surface wavelength on the surfacevofthe sonically energized liquid from which the particles were generated. Determination of such a relationship provides at once, of course, a relationship between sonic energy frequency and particle size by appropriate substitution from Equation 2 above. 7 I

In determining the relationship between surface wavelength and/or sonic frequency on the one hand and particle size on the other, sonic energy was applied directly from a transducer assembly to a molten wax for the generation of particles therefrom by spreading or flowing the wax directly onto the resonator tip. These particles were cooled and condensed, and then measured. The wax used forthe experiments was Acrawax C made by Glyco Products (30., Inc., Iew York, N.Y. This wax is a synthetic material having an unusually high and well defined melting range of 284290 F. The specific gravity of this wax, translatable to density, in the temperature range of 3 l0350 F. referred to water at 60 F., and its surface tension in this same temperature nange are quite close to those of a typical home heating oil at 100 F, the approximate temperature at which an oil of this kind is frequently atomized by traditional means such as a pressure nozzle for mixing with air and subsequent combustion; These properties, important for Equation 2, are compared in Table 1 below:

According to the experiments conducted, fog particle size was found to vary substantially linearly with wavelength. At a frequency of k.cp.s., the droplets produced were very much larger than those from a conventional oil burner nozzle. At 800 k.cp.s., however, very iine spherical particles of less than 10 microns diameter were produced. Fuel oil particles of such small sizehave been shown to burn with a flame essentially the same as that of a fuel gas. Other experimental data relating to sonic energy frequency, surface wavelength, and number median diameter of particles directly generated by sonic energy are given for Acrawax C in Table Hbelow.

Considering these data together with Equation 2, it may be seen that in view of the substantially linear variation of particle size with surface wavelength, particle size varies also substantially as the negative two thirds power of the sonic energy frequency. In the general qualitative sense, frequency must be increased to obtain a finer size of particle when the liquid to be atomized is disturbed directly by the inflow of sonic energy. With increasing frequency, openating parts become smaller, more fragile, and have less energy absorption and transfer capabilities as pointed out above. Accordingly, for the direct generation of liquid particles by sonic energy means, an effective lower limit will be placed on particle size by the lower limit of size in which the sonic energy transducer can be usefully constructed.

According to this invention, the above-described limitation of the prior art on the degree of fineness to which a liquid may be atmozied by sonic energy'means is removed by applying such energy to the liquid only indirectly. Specifically, sonic energy is employed to provide mechanical impacting of a flexible screen member on which the liquid to be atomized is coated, flowed, or wiped, and from which this liquid is discharged in the form of a fog of fine particles. With the method and appartus of this invention, the size of particles constituting the fog be determined primarily by the screen opening size or mesh rather than by the operating frequency of the sonic energy transducer. By a simple changing of screens, particles may be generated through a range of sizes with a single, rather low frequency of sonic energy.

The nature and substance of this invention will be more clearly perceived and fully understood by referring to the following description and claims taken in connection with the accompanying drawings in which:

FlGUR-El represents a side elevation view partly in section of a high frequency electronic generator coupled to a half-wave transducer assembly of a piezo-electric disc element and conical sonic energy resonator in a suitable mounting, a screen being provided closely adjacent the tip end of this resonator according to the present invention and this screen having mounting means whereby its position'relative to the transducer assembly may be finely adjusted in at least some directions;

FIGURE 2 represents a side elevation view partly in section and partly schematic of [a portion of an apparatus embodiment of this invention wherein the screen from which liquid particles are discharged is provided with mounting means allowing it to be rotated continuously across the tip of the conical sonic energy resonator for purposes of liquid feeding to this tip;

FIGURE '3 represents a side elevation View partly in section and partly schematic of a portion of an apparatus embodiment of this invention wherein the screen from which liquid particles are discharged is provided with mounting means allowing it to be translated continuously across the tip of the conical sonic energy resonator for purposes of liquid feeding to this tip;

FIGURE 4 represents a side elevation view partly in section of a half-wave transducer assembly of a piezoelectric disc element and conical sonic energy resonator with a screen closely adjacent the tip of this resonator according to the present invention, the transducer assembly being provided with an axial passage for purposes of liquid feeding to this tip, and

FIGURE 5 represents Ia side elevation view partly in section of a half-wave transducer assembly of a piezoelectric disc element and conical sonic energy resonator with a screen closely adjacent the tip of this resonator according to the present invention, the resonator being provided with connecting radial and axial passages for purposes of liquid feeding to this tip.

Referring now in detail to the drawings, especially to FIGURE 1 thereof, a high frequency electronic generator or oscillator 6 having connection to a low frequency voltage source through cable 8 and plug 10 is closely coupled on its output side by means of a cable r12 across the faces of a disc-type piezo-electric element 14 of a sonic energy transducer (15. This piezo-electric element is bonded to the larger diametral surface of a sonic energy resonator 16 of generally conical form. As assembled, piezo-electric element 14' and resonator element 16 should have an overall length which is equal to essentially one half of the wavelength of sound in the material of the resonator at the operating frequency. A full-wave transducer structure of the kind described already may, however, be used within the scope of the present invention.

For purposes of the present invention, it is not critical that generator 6 be of the electronic variety. This generator may suitably be of the rotary variety also, both varieties and their uses being well known in the sonic energy art. Likewise, the nature of piezo-elect'ric element 14- is not critical. This device may comprise any one of several materials. Use in transducers of such a piezoelectric material as the ceramic crystal barium titanate has been mentioned already. Other ceramic crystal materials suitable for this use include lead zirconates and lead zirconium t-itanates. Still other materials such as nickel and cobalt-nickel of a magnetostrictive nature may also be used in transducers.

Considering the use of a ceramic disc in a transducer assembly for exemplary purposes, however, the disc faces are silvered and then the electrical leads or lugs are soldered thereto. Next the disc must be bonded to the sonic energy resonator cone, and this bond is critical for proper operation of the transducer assembly although neither its structure nor the method of making it constitutes any part of the present invention. In joining the ceramic disc or piezo-electric element and the resonator cone, a cement such as an epoxy resin should be used which sets by polymerization rather than by solvent evaporation. A suitable elastic and electrically conductive material for the resonator cone itself is aluminum, as mentioned above. Other materials appropriate for cone 16 include brass and stainless steel. Most desirably the cone will be shaped externally with an exponential curvature, but it may also be straight-sided, and may even be fiat-sided.

In the apparatus embodiment of this invention illustrated in FIGURE 1, support for the transducer assembly is furnished from base element 18. An upwardly-extending post member 20 is threaded into a raised region 22 of base 18, and locked in place with nut 24. At its upper end, this vertical member has a transducer locating ring element 26 threaded thereonto and locked with a nut 28. This ring element encloses sonic energy resonator cone 16. The cone is maintained in spaced relation to ring 26 by means of three point-ended screws such as 30, substantially equally spaced around the ring element, and having lock nuts 32. These screws directed radially inwardly through ring 26 engage notches or drill spots in the lateral surface of the cone. All these spots should lie in a single circumferential line on the cone, and this line should coincide with the node of vibrations in the cone when the transducer assembly is energized from generator 6.

Closely adjacent the tip end of a resonator cone 16 is a screen element 34. This screen will actually be in contact with the cone tip intermittently during operation of the transducer-concentrator assembly for atomization of liquids according to the present invention, but there is no physical bond between the screen and the cone. Screen 3.4 may conveniently be of circular form, but is not required to be so configured. As shown, its edge region is slightly upset to fit closely over and extend outwardly along a shaped annular surface of frame member 36.- The screen is held tightly on and against frame 36 by means of a clamping ring 38, whereinto are threaded a plurality of thumb screws such as '40 which pass through clear holes in frame 36.

Depending on the materials and dimensions of the parts in any particular apparatus embodiment of this invention as shown in FIGURE 1, upsetting of the edge region of screen 34 may be effected in a preforming operation, or it may not be effected until the screen is compressed against frame 36 by clamping ring 38. In any case, the screen should be tight over and across the frame when parts are assembled as shown in FIGURE 1. Holes or slots in the edge region of the screen will preferably be preformed for accommodation of screws 40. The material of screen 64 is not critical for purposes of this invention so long as the composite screen is characterized by at least a degree of elasticity within a limited range of drum-like flexing. Within the scope of this very general requirement, it may be expected that screens comprising metal wires will be preferable to those comprising threads of either natural or synthetic fibres.

Extending across the lower region of frame 36, and fixedly'secured thereto by a plurality of screws suchas 42 is a rigid yoke member 44. This yoke is vertically bored to have at least one clear hole through which passes the upper threaded end of a post member 46. Yoke 44 is secured on post 46 by means of nuts 48 and 50. The lower end of post 46 is threaded into a sliding block member 52, and is locked therein by means of nut 54.

Block 52 is characterized by a guide element 56 formed on or fitted onto its lower surface. This guide element, which may be wedge-shaped in transverse section, fits closely into a groove region 58 formed in base 18. Block 52, guided by element 56 running in groove 58, may slide on surface 60 of base 18. This surface will preferably be smoothly finished as will be the surfaceof block 52 sliding upon it, and also the bearing surfaces of guide element 56 and groove region 58. I

At least one position-adjusting rod 62 is threaded into block 52, and secured therein by means of nut 64. This rod, threaded at both ends, extends horizontally through a clear hole in raised region 22 of base 18. On its threaded end extending beyond raised base region 22, rod 62 is provided with two wing nuts 66 and 68, the first of these being intended to bear against a lateral, preferably finished surface 70 of raised base region 22, and the second being intended to bear and lock against the first. A compression spring 72 encloses adjusting rod 62, and is contained between sliding block 52 and raised base region 22. The force of spring 72 acting against block 52 tends to move this block in a direction carrying screen 34 away from the tip end of sonic energy resonator cone 16.

The remaining structural item appearing in FIGURE 1 is feed tube 74 wthrough which liquid to be atomized is flowed onto screen 34. This tube has connections not shown leading to a source of liquid, a tank of home heating oil for example, these connections including appropriate pumping and metering devices. The mounting of feed tube 74 will be capable of movement so that this tube may be moved not only simultaneously with screen 34 as sliding block 52 is shifted, but also, desirably, independently of screen 34 to allow adjustment of position of the tube outlet end with respect to the screen. It is within the scope of the present invention that the liquid feed tube be positioned to flow liquid onto that side of the screen whereto the tip of the sonic energy resonator cone is more closely adjacent, as well as onto the more distant side. A feed tube 74 so positioned is indicated in dotted outline. Tubes 74 and 74 may be provided with widemouthed outlet ends to achieve good initial distribution of liquid across screen 34.

Although the machine elements which would be in volved are not specifically illustrated, it is obviously within the scope of well known art that means for recovering liquid material flowed onto but not atomized from screen 34 could be provided. Such means might includes, for example, -a drip pan located below the screen and a scraper operating across one or both faces of the screen.

Adjustment and operation of the apparatus shown in FIGURE 1 will now be considered. Locking Wing nut 68 is backed off from adjusting wing nut 66, and the latter nut is manipulated to shift sliding block 52 as necessary to bring screen 34 into at least light contact with the tip end of sonic energy resonator cone 16. Nuts 48 and 50 may be manipulated to shift yoke 44 up or down on post 46, and so adjust the vertical position of screen 34- with respect to the cone. The most desirable vertical adjustment will be determined by experience, but asa starting adjustment the screen may be approximately centered up and down with respect to the cone, substantially as shown. Although no means of making transverse adjustment of the screen are particularly illustrated, it is obvious that such means could' be provided easily if desired. However, if such means. be not provided, satisfactory results will be achieved within the scope of other adjustments if the illustrated parts are so designed that screen 34 is centered transversely with respect to resonator 'cone 16.

Screen 34 having been positionedwith respect'to resonator cone 1'6, liquid feed tube 74 is positioned with'respect to the screen. An initial quantity of liquid to be atomized may be flowed onto the screen, enough at least to provide some liquid on that partof the screen in way of the tip of the sonic energy resonator cone. The next I 7 step will be to start the generator 6 according to procedures appropriate to that piece of equipment depending upon its particular design. Such procedures do not constitute any part of the present invention. With generator 6 imposing an alternating voltage across the faces of piezo-electric element 14, there will be a flow of sonic energy into resonator cone 16. Physically, this flow will be evidenced by a rapid, though relatively minute shortening and lengthening of the cone. Actual movement of any region of cone 16 will be greatest at the tip adjacent screen 34.

The nature of the interaction between the resonator cone tip of the transducer assembly and the screen is pri marily one of the tip impacting upon the screen in the lengthening portion of the vibrator cycle of the transducer. Even though the screen be rather heavily tensioned initially across the cone tip by adjustment of block 52, its inertia will be such that it cannot follow fully the liner excursions of this tip at sonic or ultrasonic frequencies. In the shortening portion of the vibratory cycle of transducer 15, the tip of resonator cone 16 will pull back out of contact with screen 34 even though the screen flexes elastically to try to follow it, and then as the transducer goes into the lengthening portion of its vibratory cycle the cone tip will drive against the screen to distend it to the right according to the structural arrangements of FIGURE 1. It will be seen that in the course of operation of the illustrated apparatus contact between the transducer and the screen, specifically between the resonator cone tip of'the transducer assembly and the screen, exists only intermittently.

The foregoing-described impact action of thetip of resonator cone 16 upon screen 34 will cause atomization of liquid on that part of the screen generally adjacent the tip region of the cone, andwill further cause at least some net displacement discharge of this liquid from the screen as a particle fog 76. Once atomization has been started, continuous metered feeding of liquid through tube 74 onto screen 34 may be commenced for flow downward onto the screen area in way of the tip of cone 16. Wing nut 66 may be manipulated for fine adjust ment of the screen longitudinally with respect to cone 16 for optimum results. This nut should be locked with Wing nut 68 once such adjustment has been achieved.

Operating results obtained with an apparatus embodiment of this invention essentially similar to that shown in FIGURE 1 using molten Acrawax C as the liquid to be atomized are given in Table III below:

In evaluating these results, it should be observed first of all that a constant operating frequency of 15 k.c.p.s. was employed. The condition which was varied was the screening of the sonic energy resonator cone. For a first trial, no screen was used at all. This yielded particles of a mass median diameter of 112 microns. Note that particle size designation according to mass median diameter in Table III difiers from designation according to number median in Table II, mass median tending to give significantly higher values. For a second trial, a screen with comparatively coarse openings of 177 microns was used. This yielded particles of a mass median diameter of 116 microns, essentially the same as that obtained without any screen within experimental error. For a third trial, a screen with openings of 149 microns was used. This yielded particles of a mass median diameter of 100 microns, definitely smaller than that obtained without any screen. In succeeding trials, screens having openings of 105, 53 and 38 microns were used. These yielded particles of succeedingly smaller mass median diameters of 80, 63, and 31 microns.

With particle size data available from experimental trials using screens, calculations were made on the basis of the relationship developed from Table II of this specification to determine the operating frequency needed to yield these same particle sizes in the absence of any screening. The results of these calculations are given in the fourth column of Table III. To cite one example for purposes of comparison, it may be seen that for direct, unscreened atomization of molten Acrawax C, an operating frequency of 100 k.c.p.s. would be required to yield particles as fine as those obtainable using a frequency of only 15 k.c.p.s. and a screen with openings of 38 microns. From what has been pointed out already, the advantages of being able to use the lower frequency to achieve the same degree of atomization are apparent.

Referring next to FIGURE 2, a screen 78 is stretched across and retained on a frame 80 by means of a clamping ring 82 and a plurality of thumb screws 84. On its outer circumferential surface, frame 80 is fixedly fitted within the inner race of a ball bearing assembly 86. The outer race of this assembly is in turn secured to relatively rigid framework structure, such as that of an oil burner, indicated generally as 88. The inner circumferential surface of frame 80 is hobbed or otherwise machined to provide a complete annulus of gear teeth. These teeth are meshed'with those of a pinion fixedly mounted on a shaft 92 which is supported in suitable bearings not shown. Shaft 92 is operatively connected to an electric motor 94 or other suitable driving means which is shown essentially schematically, but which will in fact be supported on or from rigid structure such as 88. When motor 94 is energized to turn shaft 92 and pinion 90, the meshed connection between the teeth of the pinion and those of frame 80 will cause rotation of the frame and also of screen 78 mounted on it.

The tip of a conical sonic energy resonator 96 which is part of a transducer assembly not fully shown is positioned in intermittently contacting relation to screen 78, just as, with one limitation, the tip of resonator 16 of FIGURE '1 is or may be positioned with respect to screen 34. This limitation is that resonator 96 may not be axially aligned with the center of screen 7 8, but must be at least somewhat offset therefrom so that as frame 80 and screen 78 are turned by motor 94 there will be a sweep of screen material past the tip of the resonator. The initial rubbing pressure between screen 78 and resonator cone 96 may be adjusted by shifting the mounting of the transducer assembly, for example. This mounting is not specifically illustrated, but it should provide support for the assembly according to the principle mentioned and illustrated already, that is, essentially point support at the nodal cross-section.

Also offset from the center of screen 78 at a radius essentially the same as the oifset of resonator cone 96 is a means whereby liquid to be atomized may be applied continuously to the screen. In its illustrated embodiment, this means comprises a wick or porous Wiper 98 main- (tained in contacting relation with screen 78 by (a holder 100. This wick is saturated and steadily supplied with liquid from a source not shown as indicated by an arrow. .As screen 78 is turned by motor 94 and at least part of it rubs across wick 8, it will pick up liquid from the wick. This liquid will be carried around in front of the tip of resonator cone 98-, and there discharged as a fog of line particles 1&2. assuming that sonic energy is flowing into the resonator from a piezo-electric element not shown. It is to be understood that in place of wick 98 a continuously moistened brush, a spray nozzle, or

indeed any convenient and .suitable means for applying liquid to screen 78 at the required radius maybe used. This means may apply the liquid onto the rear side of the screen just as tube 74 does on screen 34 shown in FIGURE 1. Suitable screen scraping and drip collecting means may be provided for the recovery of liquid applied to the screen by wick 98 or its equivalent, and not subsequently atomized therefrom.

Referring next to FIGURE 3, a screen 104 in the form of an "endless belt having aregular series of perforations along each of its edges is passed over and retained on four double sprocket wheel assemblies 106, 108, 110, and 112. These assemblies will all be 'rotatably secured in some relatively rigid framework structure, such as that of an oil burner, which is not specifically illustrated. At least one of the sprocket wheel assemblies will preferably have a capability for adjustment provided in its immediate mounting so that it may be shifted in position vfor purposes of screen removal, replacement, and tensioning. As illustrated, sprocket wheel assembly 106 is opera- .tivelyconnected to an electric motor 114 or other suitable driving means which is shown essentially schemativices which maybe used. 'It is obviousthat-the liquid applying means must be in transverse alignment with the transducer assembly. It is further obvious that suitable screen scraping and drip collecting means may be provided .ior the recovery of liquid applied .tothe screen by wick 120 or its equivalent, and not subsequently atomized therefrom.

' Referring next to FIGURE 4, .a :transducer assembly 125 comprising disc-type piezoelectric element 126 and conical sonic energy resonator 128 is positioned to "bring the tip of the resonator into intermittently contacting cally, but which will in tact be supported on or from rigid structure such as that ofthe oil burner mentioned above. In respect of the screen, sprocket wheel assembly 106 is a driving means or driver. The other sprocket wheel assemblies, 108, 110, and 112, are all driven by screen 104 passing over them as this screen is itself driven by action of motor 114 imposing rotation on sprocket assembly 106.

A transducer assembly 115 comprising disc-type piezoelectric element 116 and conical sonic energy resonator 118 is positioned within the region bounded by screen 104, with the tip of the resonator being in intermittently contacting relation to screen 104, preferably in the run of this screen between driven sprocket 112 and driver sprocket 106 to insure tautness of the screen material passing in front of the resonator cone tip. The initial rubbing pressure between screen 104 and resonator cone 118 may be adjusted by shifting the mounting of the transducer assembly, for example. This mounting is not specifically illustrated, but it should provide support for the assembly according to the principle mentioned and illustrated already, that is, essentially point support at the nodal cross-section.

Also located adjacent screen 104 is a means whereby liquid to be atomized may be continuously applied to the screen. In its illustrated embodiment, this means comprises a wick or porous wiper 120 maintained in contacting relation with screen 104 by a holder 122. This wick is saturated and steadily supplied with liquid from a source not shown as indicated by an arrow. As screen 104 is turned by motor 114 and at least partof it rubs across wick 120, it will pick up liquid from the wick. This liquid will be conveyed in front of the tip of resonator cone 1-18, and there discharged as a fog of fine particles 124 assuming that sonic or ultrasonic energy is flowing into the resonator lirom piezo-electric element 116 which is in turn energized from an alternating voltage source not shown.

It is to be understood that in place of wick 98 a continuously moistened brush, a spray nozzle, or indeed any convenient and suitable means for applying liquid to screen 104 may be used. This means may apply the liquid onto the side of the screen more closely adjacent the tip of resonator cone 118 just as tube 74 does on screen 34 shown in FIG. 1. Preferably the liquid applying means will be located adjacent the run of screen 104 between driven sprocket 112 and driver sprocket 106, and above resonator cone 118. With this arrangement, the one which is illustrated, liquid from the feeding means will have to travel only a relatively short distance from relation to a partially illustrated screen 130. This screen may be taken as configured and mounted similarly to screen 34 of FIGURE 1. The assembly of piezo-electric element 126 and resonator cone .128 may likewise be 'taken as mounted similarly to the assembly of piezoelectric element 14 and resonator cone 16 of that same figure. The transducer assembly of FIGURE 4 is characterized by an axial hole 132 extending for the "full length of the assembly. At its .end opening "through the piezo-el'ectric element, this hole is provided with a sleeve fitting 134 whereonto a liquid feed tube '136 isattached. The attachment of fitting 134 onand in piezoelectric element 126 may be eifected withian epoxy resin, similarly-to the attachment of thepiezo electric element onto resonator cone 128.

Liquid to be latomized is supplied steadily to tube 136 at an appropriately regulated rate from a source not shown, as indicated by an arrow. Leaving this tube, the liquid flows through fitting 134 and hole 132 out to the region of screen which is generally adjacent the tip of resonator cone 12 8. From there the liquid will be discharged as a fog of line particles 138, assuming that sonic energy is flowing into the resonator cone from piezoelectric element 126 which is energized in turn [from an alternating voltage source not shown.

Referring finally to FIGURE 5, a transducer assembly 139 comprising disc-type piezo-electric elements 140 and conical sonic energy resonator 142 is positioned to bring the tip of the resonator into intermittently contacting relation to a partially illustrated screen 144. This screen may be taken as configured and mounted similarly to screen 34 of FIGURE 1. The assembly of piezoelectric element 140 and resonator cone 142 may likewise be taken as mounted similarly to the assembly of piezoelectric element 14 and resonator cone 16 of that same figure. characterized by an axial hole 146 in resonator cone 142 extending back from the tip thereof to essentially the nodal cross-section of this cone. At this cross-section, axial hole 146 is joined by at least one radial hole 148 extending outwardly to the surface of the cone. At its end opening through resonator cone 142, radial hole 148 is provided with a sleeve fitting 150 whereonto a liquid feed tube 152 is attached. The attachment of fitting 1-50 on and in resonator cone 142 may be efiected with an epoxy resin similarly to the attachment of transducer 140 on the resonator cone, or 'by any other suitable metal joining means such as a screwed joint.

Liquid to be atomized is supplied steadily to tube 152 at an appropriately regulated rate from a source not shown, as indicated by an arrow. Leaving this tube, the liquid flows through fitting 150, radial hole 148, and axial hole 146 out to the region of screen 144 which is generally adjacent the tip of resonator cone 142. 'From there the liquid will be discharged as a fog of fine particles 154, assuming that sonic energy is flowing into the resonator cone from piezoelectric element 140 which is energized in turn from an alternating voltage source not shown.

Although this invention has been described with a certain degree of particularity, it is to be understood that the present disclosure has been made only by way of example, and that numerous changes in the details of construction and the combination and arrangement of parts The transducer assembly of FIGURE 5 is may be resorted to without departing from the spirit and scope of this invention as hereinafter claimed. It is to be understood particularly that whereasth-is disclosure has been generally in terms of sonic energy vaporizing apparatus operating at a fundamental harmonic frequency to create a single nodal point or cross-section therein, such apparatus may be operated at higher harmonic frequencies and this invention still retain its full utility therewith. It is to be understood more particularly that for purposes of this invention the structural element described herein as a screen is not restricted to structures comprising a mesh of threads, wires, or other filament members, but is inclusive of perforated sheets, and any other areawise-discontinuous structures suitable for use. It is to be understood still more particularly that sonic energy resonator elements of other than conical tform, for example, of the form of a stepped cylinder, may be used. It is to be understood even still more particularly that the piezo -electric and resonator elements which the transducer comprises may be bonded in energy-transmitting relation by mechanical clamping rather than by the use of a cement.

What is claimed is: v

1. A method for atomizing liquids, said method com prising the steps of (l) intermittently impacting at least a part of a flexible screen member by the application of sonic energy thereto, and (2) applying liquid to be atomized onto that part of said screen member being impacted.

2. A method for atomizing liquids, said method comprising the steps of (l) intermittently impacting sequential parts of a moving, flexible screen member by the application of sonic energy thereto, and (2) applying liquid to be atomized onto those parts of said screen member being impacted.

3. A method for atornizing liquids according to claim 2 in which said screen member is moving in continuous rotation.

4. A method for atomizing liquids according to claim 2 in which saidscreen member is moving in continuous translation.

References Cited inthe file of this patent UNITED STATES PATENTS- 2,532,554 Joeck Dec. 5, 1950 2,779,623 Eisenkroft Jan. 29, 1957 2,855,244 Camp Oct. 7, 1958 2,896,922 Pohlman- July 28, 1959 2,908,443 Fruengel Oct. 13, 1959 3,067,948 Lang et al. Dec. ll, 1962 

1. A METHOD FOR ATOMIZING LIQUIDS, SAID METHOD COMPRISING THE STEPS OF (1) INTERMITTENTLY IMPACTING AT LEAST A PART OF A FLEXIBLE SCREEN MEMBER BY THE APPLICATION OF SONIC ENERGY THERETO, AND (2) APPLYING LIQUID TO BE ATOMIZED ONTO THAT PART OF SAID SCREEN MEMBER BEING IMPACTED. 